1. Field
Example embodiments in general relate to a mechanical filter-based pollution control system to remediate cooking emissions.
2. Related Art
The emission profile from commercial cooking operations has been well studied and shown to consist of particles (aerosols), semi-volatile organic compounds (sVOCs), volatile organic compounds (VOCs) and inorganic volatile species. The particles give rise to visual smoke and the VOCs give rise to odors.
The mass, size distribution and organic chemistry profile of the emissions can vary widely and are functions primarily of the type of cooking apparatus and the chemical and structural composition of the raw food being cooked. The most severe challenge to cooking emission remediation has been demonstrated repeatedly to be the emissions generated by gas char broiling of ground beef patties, with the severity of emissions being proportionately related to the fat content and the degree of well doneness of the beef patties. Of particular note is that the aerosol and chemical profiles of char broiled ground beef have been characterized and shown to not be dissimilar from the emission profile of diesel exhaust. Of particular concern are the National Ambient Air Quality Standards (NAAQS) and EPA Title V air toxics that are released. These include but are not limited to: PM2.5, PAH (poly aromatic hydrocarbons), butadienes, other toxic VOCs and ozone precursors. Indeed, air quality management districts in California are currently in the process of generating cooking emission remediation standards for charbroiling of beef, and the Bay Area Air Quality Management District (BAAQMD) has already promulgated such regulations.
Historically and currently, there are two established ways of remediating the particulate (aerosol) cooking emissions: removal from the airstream by electrostatic deposition onto alternatively charged plates or mechanical removal of the aerosols by passing the airstream through a series of progressively more efficient media filters. Established known mechanical filtration properties include impaction, interception, and interference.
Both technologies have been proven to be highly effective and there are advantages to choosing one over the other. The two main advantages of electrostatic precipitators have been first, that the pressure drop through the filters is 50-75% less than through clean mechanical filters, with that difference becoming more pronounced as the mechanical filters load. For an electrostatic precipitator the pressure drop remains constant, whereas, as mechanical filters load, the resistance to airflow increases, thus decreasing the total air that can be exhausted in the kitchen hood. This is a concern for modern day low flow hoods. This condition often mandates a constant flow control system and/or filter change warning mechanisms. Second is that the electrostatic precipitators can be programmed for nightly washing, thus removing the grease from the duct pathway and decreasing the risk of fire presented by accumulated grease in the ducted system.
Mechanical filtration control devices are often favored because they typically cost less and are more fail-safe in that electrical components are not required for proper functioning. Mechanical filters are also easier to service because highly trained technicians are not required for routing maintenance. These mechanical systems typically have three stages of progressively more efficient filters with the three stages typically in the range (all efficiencies in MERV ratings):                1. STAGE 1—MERV 6-10,        2. STAGE 2—MERV 12-15, and        3. STAGE 3—(95-99) DOP up to HEPA (99.97) DOP, wherein the numbers in parentheses represent percentage of 0.3 micrometer particles removed.        
A well established mode exists at 0.2 micrometer diameter aerosols for char broiling beef, so the stage 3 filters are mandatory. These filters are expensive so the correct selection of the workhorse filters of stage 1 and stage 2 are paramount. The frequency of filter changing varies with the cooking load; however, the optimal scenario would be a month's duration for stages 1 and 2 and a quarterly duration for stage 3.
For both types of particulate control technologies, neither one significantly effects the removal of sVOCs or VOCs. This emissions component is either ignored, or more often (especially when cooking odor abatement is desired) removed by adsorption (with varying success) by a sorbent such as activated charcoal.